Minecraft: Pi Edition is a separate release specifically for the Pi, and you can download it right here. Is there anything the humble Pi can't do? I'd recommend getting yourself one of the beefed up original boards if you're after a dedicated minecrafting machine, thanks to the doubled RAM.
The instructions for getting it up and running look pretty simple, if you're at all familiar with Linux and your Pi. So jump on over to the Pi Edition blog and get Pi-crafting right now. [Minecraft: Pi Edition, Mojang]